1. Field of the Invention
The present invention relates to a compression coding apparatus for moving picture data, and in particular, to a technique suited for use in dividing a screen and encoding the moving picture data of the divided screen in parallel by use of a plurality of encoding units.
2. Description of the Related Art
Digital video cameras are well known as a moving picture recording apparatus that has an integrated camera and that obtains an image of a subject, performs compression coding on the obtained moving picture data, and records the moving image data. Instead of traditional magnetic tape, a randomly accessible highly convenient disk medium or semiconductor memory is becoming used in a recent digital video camera. However, in general, disk media have a small amount of memory capacity, so it is necessary to perform compression coding with a high degree of efficiency.
These days, with the expectations for high image quality, a digital video camera that deals with a high-definition (HD) image, which has a larger amount of information than that of a standard image, is being developed. Therefore, also from the viewpoint of an increased amount of information of an image in itself, compression coding with a high degree of efficiency is necessary. Currently, the moving picture experts group (MPEG) scheme is often used as a standard technique for compression coding. In the MPEG scheme, encoding with a high degree of efficiency is realized by motion compensation prediction using a plurality of screens constituting a moving picture. To do this, it is necessary to process enormous volumes of image data at high speed.
If an encoding circuit operates with significantly high speed to perform the above-described high-speed processing, a problem exists in which the load becomes heavy and power consumption is increased. One example of an image coding apparatus that aims to solve this problem is described in Japanese Patent Laid-Open No. 7-095572. This apparatus solves the above problem by dividing each screen in a motion image signal into a plurality of regions and encoding the image signal divided into the regions in parallel using a plurality of encoding units.
When each screen in a motion image signal is divided into a plurality of regions and the regions are subjected to encoding in parallel by a plurality of encoding units, as described above, image quality may vary in a boundary portion of adjacent regions. The image coding apparatus described in Japanese Patent Laid-Open No. 7-095572 divides an image signal into small regions in a second division direction different from the direction of the above division and controls an encoding parameter for use by each of the encoding units for each of the small regions formed in the second division direction. The image coding apparatus makes degradation in image quality in the boundary portion of the small regions less noticeable by encoding the small regions using the same encoding parameter.
However, the image coding apparatus described in Japanese Patent Laid-Open No. 7-095572 controls the encoding parameter for each of the small regions formed by dividing of the screen in two different directions. Therefore, a predetermined set value is undesirably determined as the encoding parameter for each of the regions, so it is difficult to use an encoding parameter suited for the characteristics of an image.